Nigh Changelog here. Listed every Hero in the game and what they do. If any are not listed here, they are definitely the same as Vanilla.
Unlisted are stat changes and other smaller changes to heroes. They shouldn't be particulary noticeable right away, but I tried to make each hero of a faction feel similar enough and able to fulfill their role on the battlefield. For example, buffing a particulary frail Broken Lords or Necrophage.
XP required to level heroes reduced slightly.


Sisters of Mercy:

Valete Sapiri Kugua:
Army Boost 2; Influence Boost 3

New Hero: Lissandra Tishine
Defense Boost 2; Damage Boost 2;

New Hero: Lucy Sutame Doku
Industry Efficiency 2; Influence Boost 2


Haunts:

In addition to the 2 new Heroes, I've added a copy of Eslek Tarosh. If you do not have the achievement unlocked or usually play with the console/modding tools enabled, you should now be able to find him in the shop regardless.
This does have the side-effect that, when you can normally encounter him in the shop, the chance to find him is now a little bit higher. Should still be somewhat rare to find a Haunts hero anyway, though.

Eslek Tarosh:
Science Boost 3; Health Boost 3;

New Hero: Golmak Domar
Defense Boost 3; Army Boost 1;

New Hero: Shade Wiltenor
Dust Boost 3; Science Efficiency 1;


Broken Lords

Baron Joslyn Deyval(Starter):
Defense Boost 2; Dust Boost 2;

Duke Unwin Weybridge:
Dust Efficiency 3; Dust Boost 1

Duke Leofric Whitechapel:
Defense Boost 3

Bishop Julian:
Dust Boost 2; Influence Efficiency 2

John Port "The Shadow":
Dust Boost 2; Dust Efficiency 2; Influence Boost 1

Lord Peyton Quinn:
Damage Boost 2; Defense Boost 2;

Martin De Ildan De Suluzzo(Main Quest Hero):
Initiative Boost 3; Influence Boost 3;

Samhane Haligtide:
Attack Boost 2; Damage Boost 2; Soul Leech; Life Drain 3;


Wild Walkers

Tlato Mosi Pakwa(Starter):
Army Boost 2; Industry Efficiency 2;

Soyala Tocho:
Food Efficiency 2; Industry Boost 2;

Citli Owaci:
Attack Boost 3

Temoc Rayen:
Initiative Boost 3; Damage Boost 1;

Wayra Sigo:
Industry Efficiency 3;

Ipsa Wacha:
Food Efficiency 1; Industry Boost 3;

Ahote Zaltana(Main Quest):
Industry Efficiency 3; Industry Boost 1;


Necrophages

Feeds on Bones(Starter):
Attack Boost 2; Food Boost 2;

Long Fangs:
Attack Boost 3; Health Boost 1;

Empty Belly:
Food Boost 3; Slavery;

Never Rests:
Industry Boost 3; Slavery;

Queenslayer:
Food Efficiency 3; Industry Boost 1;

Strikes Far:
Health Boost 3; Damage Boost 1;

Ka-Riss(Main Quest):
Food Efficiency 3; Slavery;


Ardent Mages

Zarcha Attinul(Starter):
Initiative Boost 2; Science Efficiency 2;

High Inquisitor Asalah Arca:
Damage Boost 3; Science Boost 3;

Sunseeker Zakiya Eli:
Army Boost 2; Initiative Boost 2;

Nahla Al-Jazar:
Science Boost 2; Science Efficiency 2;

Wadeha Hakan:
Attack Boost 3;

Argbadh Bose Falhala:
Science Boost 3; Science Efficiency 1;


Vaulters

Petrov Judit(Starter):
Defense Boost 2; Science Efficiency 2;

Rill Kata:
Attack Boost 3; Vision Range 2;

Nadjne Zolya:
Defense Boost 2; Army Boost 2;

High Protector Toth Istvanka:
Defense Boost 3; Science Efficiency 3;

Pecs Kerre:
Industry Boost 3; Science Boost 1;

Chief Sapper Liszt Ajandek:
Fortification Boost 3; Science Boost 3;


Roving Clans:

Siryi Alastra(starter):
Health Boost 2; Dust Boost 2;

Bazi Safar Bahas:
Initiative Boost 3; Attack Boost 1;

Illegra Mordicant:
Initiative Boost 1; Health Boost 3;

Bela "The Bat" Sirlav:
Dust Efficiency 1; Food Boost 3;

Master Neqra Zeban:
Dust Efficiency 3; Dust Boost 1;

Jasah Murdap:
Dust Efficiency 2; Food Boost 2;


Drakken

Archivist Nachampassessa(Starter):
Health Boost 2; Influence Boost 2;

Archivist Jiraduveja:
Food Efficiency 3; Influence Boost 2

Lorekeeper Lakaspassar:
Health Boost 3; Army Boost 1;

Loremaster Jayawardene:
Health Boost 2; Damage Boost 2;

Lorekeeper Masargaka:
Army Boost 3

Loremaster Semsanitnwona:
Influence Efficiency 3; Food Boost 1;

Researcher Namkang:
Influence Efficiency 1; Food Boost 3;


Cultists

Andom the Seer(Starter):
Damage Boost 2; Influence Boost 3;

Urol the Speaker:
Defense Boost 2; Health Boost 2;

Edra the Listener:
Damage Boost 3; Defense Boost 1;

Tinu the Chosen:
Influence Efficiency 3; Health Boost 3;

Exid the Chosen:
Influence Boost 2; Industry Efficiency 2;

Ozek the Chosen:
Influence Boost 3; Influence Efficiency 1;


Mezari

Avara Lasmak(Starter):
Initiative Boost 2; Science Efficiency 2;

Commander Irjsko Lasmak:
Industry Efficiency 2; Attack Boost 3; Science Boost 2;

Sable Deceiver Bayari Kulaa:
Fast Learner 2; Dust Efficiency 3; Initiative Boost 2;


Forgotten:

Third Builder Gula Yawa(Starter):
Attack Boost 2; Dust Boost 3;

Sable Blade Ayou Addo:
Damage Boost 3; Initiative Boost 1;

Consecrate Mawusi Boakye:
Dust Boost 3; Influence Efficiency 3;

Sable Deceiver Napog Dauda:
Dust Efficiency 3; Initiative Boost 3;

Skya Keeper Dabuo Ofosu:
Dust Efficiency 3; Dust Boost 3;

Efalo Tegret:
Damage Boost 3; Attack Boost 1;


Allayi:

Samos Leaper Greenblade:
Initiative Boost 2; Vision Range Boost 2;

Xoyos Brightslash(Starter):
Industry Boost 2; Health Boost 2;

Breyos Master Icespear:
Science Boost 2; Expansion Support 2; Food Boost 2;

Rabos Rockstriker Highridge:
Army Boost 2; Industry efficiency 3; Science Boost 1;

Ystros Watcher Firespike:
Expansion Support 2; Industry Boost 3; Science Boost 2;

Eayos Sniffer Redpoint:
Health Boost 1; Initiative Boost 3;


Morgawr

Cetassa:
Fast Learner 1; Influence Efficiency 3; Fortification Boost 2;

Strio:
Initiative Boost 2; Health Boost 2;

Sclera:
Fortification Boost 3; Influence Boost 3; Industry Efficiency 1;

Ploria:
Fast Learner 1; Initiative Boost 3; Defense Boost 1;

Iracu(Starter):
Defense Boost 3; Influence Efficiency 2;

Difore:
Fast Learner 1; Health Boost 3; Fortification Boost 3;


Kapaku:

Makani Chay(Starter):
Army Boost 2; Industry Boost 2;

Ululani Raui:
Industry Efficiency 2; Industry Boost 2;

Takari Mu:
Defense Boost 3;

Grand Cleric Akuma:
Science Efficiency 3; Food Boost 2;

Pali Inoa:
Initiative Boost 2; Attack Boost 2;

Shaman Rawiri:
Industry Efficiency 3; Food Boost 1;

Haukea Wai(Main Quest):
Fast Learner 2; Attack Boost 3;


Mykara

Specialized Polyp 9S(Starter):
Army Boost 2; Food Efficiency 2;

Specialized Polyp 2D:
Industry Efficiency 2; Food Boost 3;

Specialized Polyp A7:
Food Efficiency 3; Food Boost 1;

Specialized Polyp 5X:
Dust Boost 3; Food Boost 2;

Specialized Polyp Q9:
Defense Boost 2; Attack Boost 2;

Specialized Polyp 3G:
Army Boost 3; Vision Range Boost 1;

Specialized Polyp Z4(Main Quest)???:
Damage Boost 2; Fast Learner 2;